Rotary engines and Stirling engines have been known for a long period of time. However, they were not applied on a very wide basis despite the fact that they provide some very significant advantages in comparison to other internal combustion engines.
The rotary (Wankel) engine has been applied as a power plant in a relatively small numbers despite its very favorable power to volume ratio and relative simplicity. Current emission standards and growing concerns about environmental pollution further decrease prospects for this type of engine which produces very low inertia, centrifugal, and friction loses.
On the other hand, Stirling cycle engines enable a clean combustion but have very unfavorable power to volume ratio. A Stirling engine which applies double-acting pistons and swash plate can operate at 3,000 rpm with an efficiency of 30% which is as good as most internal combustion engines. This engine is very easy to start, clean, quiet in operation, and relatively simple in basic design but relatively unsuitable for use as a vehicle's power plant.
Consequently, due to their drawbacks both types of engines do not seem to have a promising future as vehicle's power plant. Therefore, it is an object of the present invention to provide an hybrid engine which will eliminate drawbacks of both rotary and Stirling engines and use their advantages to provide an environmentally clean, fuel-efficient, quiet, compact, and relatively simple engine.